How to Wire a K40 Speech Processor

Written by jason parnell
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How to Wire a K40 Speech Processor
Wiring a K40 microphone (repair of an old radio receiver 1. image by wrangler from Fotolia.com)

The K40 Voice Processor is a microphone that compensates for either the loudness or softness in speech to provide a flat volume response. Popular with CB and ham radio operators, this microphone often requires special installation and wiring depending on the type of transceiver you employ. Many users of the K40 seek out the original microphone that was sold with a 40-channel radio. As second-hand items rarely include documentation, the installation and wiring are often difficult for the hobby CB user.

Skill level:
Easy

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Things you need

  • 25-watt soldering iron
  • Rosin-core solder

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Instructions

  1. 1

    Consult included documentation and circuit diagrams to determine the switching system that your CB transceiver employs: electronic, direct relay, transistor relay or power switching. This documentation also indicates the receive line, transmit line, relay coil, +12 volts line, and audio line of your CB transceiver.

  2. 2

    Solder the colour-coded wires to your electronic switching receiver array using your 25-watt soldering iron and rosin-core solder in the following manner: shield to ground, black to ground, blue to receiving line, red to transmit line, and white to audio line. Disregard the yellow lead. Leave the internal white jumper located in your K40 microphone in position 1.

  3. 3

    Solder the colour-coded wires to your direct relay receiver array in the following manner: shield to ground, black to ground, red to relay coil, and white to audio line. Disregard the blue and yellow leads. Leave the internal white jumper located in your K40 microphone in position 1.

  4. 4

    Solder the colour-coded wires to your transistor-driven relay receiver array in the following manner: shield to ground, black to relay coil, red to +12 Volts, and white to audio line. Disregard the blue and yellow leads. Leave the internal white jumper located in your K40 microphone in position 1.

  5. 5

    If your transceiver employs power switching, then solder the colour-coded wires to your receiver array in the following manner: shield to ground, black to +12 Volts, blue to transmit line, red to receive line, and white to audio line. Disregard the yellow lead. Leave the internal white jumper located in your K40 microphone in position 2.

Tips and warnings

  • Some manuals for the K40 microphone provide lists that cross-reference printed numbers and colour-coded wires, indicating where the wires go for specific makes and models of transceivers.
  • Always solder in a well-ventilated open area due to the resultant toxic fumes.
  • Always insulate any disregarded leads.
  • Do not attempt to wire a K40 Voice Processor to tube-type transceivers.

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